The present invention relates generally to electroacoustic transducers and, more particularly, to high frequency electroacoustic transducers of the type driven by or driving a piezoelectric element that bends in response to electrical energy applied across it, or which produces electrical energy in response to bending or warping.
Reference is made to the applicant's U.S. Pat. Nos. 4,845,776 issued Jul. 4, 1989 and 4,996,713 issued Feb. 26, 1991, the disclosures of which are hereby incorporated by reference with respect to the descriptions therein of such electroacoustic piezoelectric transducers.
A piezoelectric element of the type conventionally used in such electroacoustic transducers comprises a pair of piezoelectric wafers having outer electrodes which are sandwiched over a conductive metallic inter-layer which forms an electrode between the two wafers. The piezoelectric element has a substantially planar configuration and is relatively thin between its outer electrodes with respect to its lateral dimension thereby permitting the element to flex along its long dimensions or diameters. When an electrical signal is positive on the outer electrodes with respect to the intermediate electrode, the center of the piezoelectric element flexes in one direction. Reversing the electric field polarity causes the piezoelectric element to flex in the opposite direction. Impressing an alternating voltage across the electrodes causes the piezoelectric element to oscillate.
Electroacoustic piezoelectric transducers are known which convert alternating electric voltage to sound, thereby acting as loudspeakers. Such piezoelectric loudspeakers generally operate in high frequency ranges and are commonly known as "tweeters."
Conventional piezoelectric tweeters generally comprise a housing which encloses a diaphragm mounted for vibration, a piezoelectric element coupled to the diaphragm, and an adjacent electric conductor coil structure, which may comprise the coil of an air core transformer in an electrical circuit. The housing of the tweeter must be relatively large in its height dimension in order to accommodate the coil structure and the adjacent diaphragm.
High frequency loudspeakers or tweeters are used both by themselves, i.e., separate from low and mid-range speakers, as well as in systems in which they are physically coupled to low and/or mid-range loudspeakers. For example, a loudspeaker assembly may comprise a loudspeaker that reproduces low frequency sounds, on which is mounted one or more additional loudspeakers for reproducing medium and high range frequency sounds. However, such combined speaker construction often presents difficulties in cases where the space for mounting the speakers is limited such, for example, as in the case of automobile sound system speakers.
It is not uncommon for the loudspeakers of automobile sound systems to be mounted within the thickness of the automobile's doors. The space available for the speakers within an automobile door is generally limited since other components, such as electrical window-lifting mechanisms and door locks, among other things, are also housed within the door thickness. A problem therefore arises in situating a combined speaker construction within the door of an automobile in view of the limited space available and the relatively large height dimensions of the tweeter. In the past, the problem of limited space has been solved by using speakers having smaller dimensions and, therefore, less power and/or reduced quality, than would otherwise be desired.